Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B25/00—Screws that cut thread in the body into which they are screwed, e.g. wood screws
  • F16B25/10—Screws performing an additional function to thread-forming, e.g. drill screws or self-piercing screws
  • F16B25/103—Screws performing an additional function to thread-forming, e.g. drill screws or self-piercing screws by means of a drilling screw-point, i.e. with a cutting and material removing action
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/36—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases using ionised gases, e.g. ionitriding
  • C23C8/38—Treatment of ferrous surfaces
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/80—After-treatment
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B25/00—Screws that cut thread in the body into which they are screwed, e.g. wood screws
  • F16B25/001—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by the material of the body into which the screw is screwed
  • F16B25/0031—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by the material of the body into which the screw is screwed the screw being designed to be screwed into different materials, e.g. a layered structure or through metallic and wooden parts
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B25/00—Screws that cut thread in the body into which they are screwed, e.g. wood screws
  • F16B25/0036—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by geometric details of the screw
  • F16B25/0042—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by geometric details of the screw characterised by the geometry of the thread, the thread being a ridge wrapped around the shaft of the screw
  • F16B25/0057—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by geometric details of the screw characterised by the geometry of the thread, the thread being a ridge wrapped around the shaft of the screw the screw having distinct axial zones, e.g. multiple axial thread sections with different pitch or thread cross-sections
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B33/00—Features common to bolt and nut
  • F16B33/008—Corrosion preventing means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
  • F16B33/00—Features common to bolt and nut
  • F16B33/06—Surface treatment of parts furnished with screw-thread, e.g. for preventing seizure or fretting

Definitions

• the present invention relates to a screw.
• the invention particularly has in view two types of screw, namely self-drilling screws intended to secure sheet metal, especially stainless sheet metal, on roofs and house frontages, and self-tapping screws.
• a multiplicity of demands, several of which are difficult to reconcile, are placed on a self- drilling screw intended to act as a securing element for stainless sheet metal on roofs and house frontages: - the material shall have a cold workability such that it can be shaped in the cold condi ⁇ tion into a screw having a tip which can drill the screw through a sheet of stainless steel,
• the screw or at least a surface layer thereof, and especially the surface of the screw tip, shall possess a very high degree of hardness, - the screw shall possess very good inherent resistance to corrosion and no stress corro ⁇ sion shall arise as a result of galvanic reactions between the screw and the stainless sheet metal,
• the screw head shall, for aesthetic reasons, be of the same colour as the sheet metal, - the screw must not be too expensive.
• One object of the invention is to provide a screw of such a material, and treated in such a manner, that it fulfils all the requirements that are placed on self-drilling screws which are intended to be used as securing elements for stainless steel facings for roofs or frontages.
• the screw shall possess a very high degree of hardness, at least in a surface layer thereof, in order to be able to function as "its own thread tap" in order to produce threads in a drill hole.
• the screw is to be used as a securing element for stainless sheet metal or other stainless elements, the same demands are placed on it in terms of corrosion re ⁇ sistance as are placed on self-drilling screws.
• Fig. 1 shows a self-drilling screw of a design which is known per se, to which the in- vention can be applied;
• Fig. 2 shows diagrammatically, and on a very large scale, the structure of a surface layer of the screw, and
• Fig. 3 illustrates how the screws can be arranged in a fixture during a treatment step.
• the matrix of the screw 1, i.e. the whole screw with the exception of the surface layer, consists of austenitic stainless steel.
• the steel has a high content of chromium and nickel and a low content of carbon, i.e. max 0.1 % C, preferably max 0.05 % C; 18-25 % Cr; and 8-20 % Ni.
• the steel can contain other alloying ele ⁇ ments, for example up to a maximum of 10 % Mo.
• the steel also contains a certain quantity of copper, suitably 2-4 %, in order to improve the cold workability of the steel.
• a suitable composition is 0.01 % C, 0.5 % Si, 0.6 % Mn, 18 % Cr, 9.5 % Ni, and 3.5 % Cu, balance iron and impurities.
• austenitic stainless steels possess a very high degree of corrosion resistance and a good level of toughness and cold workability, but are of low hardness.
• the matrix of the screw has a hardness which does not exceed 250 HV.
• the screw was surface hardened by means of so-called ion nitriding, also termed plasma-nitriding.
• ion nitriding also termed plasma-nitriding.
• a plasma in other words an ionized gas
• the screws are placed in a suitable fixture which, in turn, is placed in a furnace which is filled with a mixture of nitrogen and hydrogen gases. A voltage of 1000 V is applied between the screws and the furnace wall.
• a problem with ion nitriding is that the passivation layer of the stainless austenitic steel is partially destroyed by the ionic bombardment, resulting in a lowering of the corrosion resistance.
• the ion nitrided screws are - in accordance with one embodiment - covered with a thin layer of zinc by an elec ⁇ tro-plating treatment.
• This zinc layer 4 has a thickness of at least 5 ⁇ m, preferably of at least 8 ⁇ m, but does not exceed 25 ⁇ m in thickness.
• An additional effect of the zinc layer is that it imparts lubricating properties to the screw, which properties are advantageous when the screw is to be used as a self-drilling screw.
• the zinc layer also provides the screw with an aesthetically appealing surface and colour.
• the galvanization is expe ⁇ trans performed by means of a dipping process in an acidic zinc bath after pickling in an acid bath in order to remove oxides on the surface of the screw.
• the zinc layer too, can have certain defects.
• the zinc layer can, in an additional operation, be coated with a very thin layer of chromium 5.
• This layer typically has a thickness of 1-5 ⁇ m, or approxi ⁇ mately 2 ⁇ m.
• the chromating can be carried out by depositing 3-valent chromium - so- called blue chromate - by a dipping process lasting approximately 1 minute.
• the screw heads can be covered with a layer of lacquer, expediently a polyester lacquer which is sprayed onto the heads in powder form, after which the lacquer is hard ⁇ ened in a manner which is known per se.
• This layer of lacquer improves the corrosion protection still further on that part which remains exposed while, at the same time, by appropriate choice of lacquer colour, a screw can be obtained which completely harmo- nizes with the sheet metal in which it is to be used.
• the screw can, after the ion nitriding and pick ⁇ ling, be electrolyte polished, i.e. treated in an electrolytic bath in accordance with princi ⁇ ples which are known per se, so that a very thin layer is removed from the rough surface resulting from the ion nitriding. It is particularly the peaks on the surface which are re ⁇ moved so that an even surface finish is obtained. While the surface-hardened layer re ⁇ sulting from the ion nitriding has a thickness of 0.01-0.2 mm, with an average depth of about 0.05 mm, the surface layer removed by the electrolyte polishing amounts to a maximum of only 20 ⁇ m, normally from 5 to 10 ⁇ m. Use of this treatment means that the abovementioned galvanization can be dispensed with for certain applications. If so de ⁇ sired, the electrolyte polished screw can of course also be provided with a suitable lac- quer paint.
• the fixture consists of a flat box 11 with a plane bottom 12 which is provided with small orifices 13 for the screws 1 which are to be ion nitrided.
• a plate 14 the thickness of which determines the height of the screw heads above the bottom 12.
• the plate 14 has through-holes 16 immediately opposite the holes 13 in the bottom 12.
• the screws which are to be ion nitrided are mounted in the holes 16, 13, after which the box 11 is covered by a lid 17. Both the box 11 and the lid 17 are made of metal and form an anti-ionization screen for the screw heads 6 and for those parts of the shank 7, Fig.
• each screw 1 which are located inside the fixture 10, i.e. within the area of the holes 13 and 16.
• this area has been designated 9 in Fig. 1.
• the only part of each screw 1 which is exposed to the plasma-nitriding is thus the drilling screw tip 2 and the remainder of the shank 7, i.e, the section 8.
• the screws were provided with a thin layer of zinc by galvanic treat ⁇ ment in order, finally, to be chromated in the same way as has been described above. In this case, therefore, the structure of the surface layer which is shown in Fig.
• test No. 1 5 screws were tested which were made of stainless steel having the follow ⁇ ing composition: 0.01 % C, 0.5 % Si, 0.6 % Mn, 18 % Cr, 9.5 % Ni and 3.5 % Cu, bal ⁇ ance iron and impurities.
• the screws were mounted in a fixture of the above-described type, after which the tips 2 and the lower part 8 of the screw were subjected to ion nitriding. The screws were then allowed to cool in air, after which they were pickled.
• Clark's solution (37 % HC1, 20 g/1 Sb2 ⁇ 3 and 50 g 1 SnCl2) was used as the pickling solution. After the pickling, the samples were thoroughly rinsed with pure water. The whole of each screw was zinc-coated galvanically in the manner which has been de ⁇ scribed above such that the screw head, the shank and the tip all received a zinc layer which was at least 5 ⁇ m in thickness.
• test No. 2 5 screws were tested which were made of stainless steel of the ASTM 305 type having the nominal composition of maximally 0.06 % C, 18.5 % Cr and 11.5 % Ni, balance iron and impurities. These screws were not ion nitrided and nor were they oth- erwise surface-hardened. However, the screws were pickled and coated with zinc gal ⁇ vanically in the same manner as was employed for the sample preparation for test No. 1.
• test No. 3 10 screws were tested which were made of the same steel as in test No. 1.
• the screws were ion nitrided in a screening fixture in the same manner as for the sample preparation for test No. 1, and were pickled but not coated with zinc

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Geometry (AREA)
• Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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Publications (1)

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Cited By (10)

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Citations (2)

• 1994
  • 1994-05-03 CA CA 2160793 patent/CA2160793A1/en not_active Abandoned
  • 1994-05-03 JP JP6524178A patent/JPH08509799A/ja active Pending
  • 1994-05-03 WO PCT/SE1994/000400 patent/WO1994025764A1/en not_active Application Discontinuation
  • 1994-05-03 AU AU66617/94A patent/AU6661794A/en not_active Abandoned
  • 1994-05-03 EP EP94915315A patent/EP0697072A1/en not_active Withdrawn

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